The specific aim of this project is to design, construct, characterize, and evaluate in tissue and in animal a novel fiberoptic catheter and Diode laser energy source for the percutaneous treatment of ventricular tachycardia. The proposed system is expected to allow suitable patients to undergo a minimally invasive procedure for the treatment of cardiac arrhythmias in the catheterization laboratory. This can result in substantial benefit to the patient and a significant reduction in the cost of health care for this ailment. The proposed catheter employs a proprietary fiberoptic delivery system that is integrated into a multi-polar electrophysiologic mapping catheter. When coupled to a Diode laser, operating in the wavelength range of 810 to 950 nanometers, this catheter is expected to generate suitable lesions in the ventricular wall thus causing effective treatment of the diseased tissue. The mapping capability of this catheter serves to identify the source of arrhythmia and provides feedback means for the control of laser energy. The basic design objective is to create a laser delivery system that is integrated in a 2.66 millimeter diameter catheter having sufficient flexibility and directionability to permit percutaneous introduction and effective electrophysiologic mapping simultaneous to the delivery of laser energy. PROPOSED COMMERCIAL APPLICATION: By providing less invasive means for the treatment of ventricular tachycardia, the proposed laser catheter offers a viable alternative to implantable defibrillators and cardiac surgery. Laser ablation can be performed percutaneously during electrophysiologic mapping thus reducing the cost of treatment and improving the quality of outcome to the patient. The worldwide market for this product is estimated at 400 million dollars.